The bill is useful, but juvenile Curlews have a shorter bill, so there can be similarities. Most Whimbrel have a bold stripe on the side of the crown, and show an obvious pale supercilium. The bill length, together with Whimbrel's bold face pattern usually sorts them out easily.

It's worth pointing out that this bird has its head at a slight angle away, so that the beak looks shorter than normal.

Yes...it is! Whimbrel are actually quite different, being smaller birds overall with a shorter bill and bolder head pattern. As usual, though, these things are only obvious with a really good view, like these pictures. There are often cases of a distant bird on an estuary, or something similar, where it can be quite tricky to be sure.